There is an increasing demand for olefins in the chemical industry. In particular olefins such as ethylene, propylene, and butadiene are of commercial importance since they are used as building block chemicals for the preparation of petrochemicals and polymers. Ethylene and propylene are used for the production of polyethylene and polypropylene respectively, whereas butadiene is used for the production of polybutadiene and styrene-butadiene-rubber (SBR).
Processes for the preparation of olefins are known in the art. A major process for the preparation of olefins is the steam cracking of a paraffin-containing hydrocarbon feedstock such as naphtha, gas oil, ethane, propane and butane. Besides ethylene and propylene, these steam cracking processes also produce substantial amounts of butadiene, typically obtained as part of the C4 product fraction of the steam cracker product. The butadiene is retrieved from the C4 product fraction by extraction.
In recent years, other processes for the preparation of olefins have been developed, including oxygenate-to-olefins (OTO) processes. These processes typically produce more propylene than the earlier mentioned steam cracking processes and are therefore seen as a suitable means to provide a uniform product slate, i.e. comprising significant amounts of both ethylene and propylene.
In US 2010/0206771 A1, an integrated process for producing hydrocarbons, in particular C2-C4 has been described, using a combined plant with a steam cracker and a methanol-to-propylene (MTP) process, wherein the respective intermediate product streams of the steam cracker and the MTP are combined completely.
A disadvantage of the process of US 2010/0206771 is that the MTP product stream does not contain butadiene, as can be seen from Table 1 of US 2010/0206771. Consequently, the butadiene content in the steam cracker product stream is diluted by combining the steam cracker product stream with the MTP product stream. The efficiency of the butadiene extraction from the product is dependent on the butadiene concentration, whereby the efficiency of extraction decreases with decreasing butadiene concentration. As a result of the dilution of the butadiene concentration, less butadiene is extracted. Moreover, as part of the C4 product fraction is recycled to either the steam cracker or the MTP process, the remaining butadiene in the C4 product fraction is hydrogenated and thus must be considered lost. At the same time hydrogen and sufficient hydrogenation means must be provided to hydrogenate the residual butadiene.
Such a process leaves room for improvement in terms of butadiene recovery and hydrogen consumption.
Object of the present invention is to provide an integrated process of a steam cracker process and an OTO process for producing olefins in which the overall butadiene yield is improved.